Electrical activity of the heart produces weak magnetic fields which emanate out of the body intact and are currently being measured with cryogenic SQUID magnetometers. These measurements, called magnetocardiogramas (MCG), are very similar to electrocardiograms (ECG) and are 100% non-invasive and benign. Their clinical applications are being explored and have the potential tot supplement or replace surgical catheter procedures to localize sites of abnormal electrical activity in the heart. Potential applications include non-invasive detection and localization of arrhythmias, ventricular infarcts, and pre-excitation (His bundle) pathway abnormalities. The cryogenic SQUID instruments are very expensive ($3 million) and thus are not widely available for medical use. A lower cost alternative would make these procedures more readily available and offer a-significant advance in diagnostic and preventative health-care. The proposed fiber-optic biomagentometer will be inexpensive, operative at room temperature, does not require any shielding, will be easier to use and portable. The Boeing Co. over the last 10 years has developed portable room- temperature fiber-optic magnetic sensors for submarine detection in shallow coastal waters. These sensors operate without any shielding and are inexpensive (approximately $2 k/sensor). We have recently shown that the same submarine detection sensor is also capable of detecting the cardiac magnetic fields. Thus, it has potential to detect biomagnetic fields. Thus, it has a potential to detect biomagnetic fields. We need to explore ways to adopt this technology for medical applications. Our objectives are to design and test such a sensor to detect the biomagnetic signals reliably, and with the same sensitivity and fidelity as a SQUID biomagnetometer. We will demonstrate the feasibility of building multiple sensor (1-3) arrays which could map the magnetic field of the whole heart with a good spatial resolution. This will also be a good example of converting a defense technology to medical applications. Other applications: There are non-contact, leadless measurements. Examples include: (1) fetal heart monitoring; (2) Emergency Medicine: non-contact monitoring of the heart rate of born patients; 93) Rehabilitation Medicine: localization of site of the abnormal electrical activity of limbs and torso skeletal muscles for non-invasive clinical diagnostics; (4) Brain response (MEG) measurements for localization of epileptic foci. Our long range goals are to develop an inexpensive 50-60 channel (approximately $100 k) fiber-optic biomagnetic sensor system for mapping the magnetic field of the whole heart under normal and disease conditions, and develop related appropriate technologies for its clinical uses. It will lead towards an affordable non-invasive cardiac biomagnetic imaging system. Other uses will also be explored.